1. Field of the Invention
The invention relates to a liquid crystal material contained in a polymer/liquid crystal composite including the liquid crystal material and a polymer for use in an element driven in a state of an optically isotropic liquid crystal phase, wherein the liquid crystal material exhibits the optically isotropic liquid crystal phase in the temperature range of approximately 5° C. or more in the elevated temperature process but does not exhibit a nematic phase; and a mixture comprising a liquid crystal material and a monomer, the polymer/liquid crystal composite and a liquid crystal element using the composite thereof.
2. Related Art
When a nematic liquid crystal compound/composition is heated in a state where a nematic phase is exhibited, an isotropic phase is gradually appeared. In such an isotropic phase in a nematic liquid crystal compound/composition (hereinafter sometimes referred to as “non-liquid crystalline isotropic phase”), the Kerr effect, which is a phenomenon in which a value of electric birefringence ΔnE (a value of birefringence induced when electric field is applied on an isotropic medium) is proportional to the square of electric field E [ΔnE=KλE2 (K: Kerr constant (Kerr coefficient), λ: wavelength)], is observed. Specifically, a high Kerr constant is observed at a temperature just above the nematic phase-isotropic phase transition temperature. It is thought that the Kerr effect is attributed to the presence of short range order of nematic molecular alignment generated by heat fluctuation in a non-liquid crystalline isotropic phase.
In the case of a liquid crystal material, the Kerr effect is observed not only in a non-liquid crystalline isotropic phase but also in a blue phase. A blue phase is generally exhibited between a chiral nematic phase and a non-liquid crystalline isotropic phase, and in general, the temperature range thereof is very narrow (about approximately 1 to approximately 2° C.).
On the other hand, in a composite material of a polymer and a chiral liquid crystal, an “optically isotropic liquid crystal phase (a phase in which liquid crystal molecular alignment is macroscopically isotropic, and liquid crystalline order is microscopically present)” is exhibited in a relatively wide temperature range, and in such a phase, the Kerr effect with a high Kerr constant has been observed (for example, see Japanese Laid-Open Patent Publication No. 2003-327966; Nature Materials, 1, 64-68 (2002); Advanced Materials, 17, 96-98 (2005); and Advanced Materials, 17, 2311-2315 (2005)).
However, though an optically isotropic liquid crystal phase is exhibited in a wide temperature range in the case of such a composite material, there is a problem that birefringence may remain even if returning to a liquid crystalline state, in which electric field is not applied, after application of high electric field. Therefore, in the case of liquid crystal elements such as indicating element, use of a composite material with a polymer is limited.